Radiation Effects on Pure-Silica Multimode Optical Fibers in the Visible and Near-Infrared Domains: Influence of OH Groups

Cosimo Campanella,Gilles Mélin,Adriana Morana,Vincenzo De Michele,Youcef Ouerdane,Emmanuel Marin,Aziz Boukenter,Sylvain Girard,Thierry Robin

doi:10.3390/app11072991

Abstract

Signal transmission over optical fibers in the ultraviolet to near-infrared domains remains very challenging due to their high intrinsic losses. In radiation-rich environments, this is made even more difficult due to the radiation-induced attenuation (RIA) phenomenon. We investigated here how the number of hydroxyl groups (OH) present in multi-mode (MM) pure-silica core (PSC) optical fibers influences the RIA levels and kinetics. For this, we tested three different fiber samples: one “wet”, one “dry” and one with an intermediate “medium” OH content. The RIA of the three samples was measured in the 400–900 nm (~3 eV to ~1.4 eV) spectral range during and after an X-ray irradiation at a dose rate of 6 Gy(SiO2) s−1 up to a total accumulated dose of 300 kGy(SiO2). Furthermore, we evaluated the H2-pre-loading efficiency in the medium OH sample to permanently improve both its intrinsic losses and radiation response in the visible domain. Finally, the spectral decomposition of the various RIA responses allows us to better understand the basic mechanisms related to the point defects causing the excess of optical losses. Particularly, it reveals the relationship between the initial OH groups content and the generation of non-bridging oxygen hole centers (NBOHCs). Moreover, the presence of hydroxyl groups also affects the contribution from other intrinsic defects such as the self-trapped holes (STHs) to the RIA in this spectral domain.

Highlights

8a,show we show thattreatment the treatment no significant on theofshape of ation-induced absorption but it slightly influences the relative magnitudes of the absorpthe radiation-induced absorption but it slightly influences the relative magnitudes of the tion bandsbands used in the in decomposition
The X-ray irradiation at 6 Gy(SiO2 ) s−1 up to 300 kGy(SiO2 ) shows a monotonic increase of the vis-near IR radiation-induced attenuation (RIA) for the low- and high-OH samples, while a different behavior was observed for the medium-OH, depending on the spectral range of interest: a monotonic increase of the RIA for wavelengths below ~600 nm and a non-monotonic behavior for wavelengths above ~600 nm
The spectral decomposition of the RIA highlighted the various point defects that contribute to the spectral absorption

Summary

Introduction

If most of today’s applications are focused on the use of single-mode (SM) or multimode (MM) optical fibers in the infrared domain (IR, 1 to 1.6 μm) targeting data communications and sensing [1,2,3,4], there is a need for waveguides able to operate in the ultraviolet, visible, and near-infrared domain (UV-Vis-near-IR from 350 to 1000 nm). As an example, such MM fibers are or will be integrated in the plasma diagnostics of fusion-devoted facilities such as ITER, National Ignition Facility (NIF), or

Methods

Results

Conclusion